This invention relates generally to centrifugal machines, and in particular to a diffuser vane seal for a variable width diffuser in a centrifugal compressor of the type used in refrigeration and air conditioning systems.
Flow stabilization through a centrifugal vapor compressor is a major problem when the compressor is used in situations where the load on the compressor varies over a wide range of volumetric flow rates. The compressor inlet, impeller, and diffuser passage must be designed to accommodate the maximum volumetric flow rate through the compressor. However, if the compressor inlet, impeller, and diffuser passage are designed to accommodate the maximum volumetric flow rate then flow through the compressor may be unstable when there is a relatively low flow rate therethrough. As volumetric flow rate is decreased from a relatively high stable range of flow rates, a range of slightly unstable flow is entered. In this range there appears to be a partial reversal of flow in the diffuser passage which creates a noise and lowers the efficiency of the compressor. Below this slightly unstable flow range, the compressor enters what is known as surge, wherein there are periodic complete flow reversals in the diffuser passage that decrease the efficiency of the compressor and which may degrade the integrity of compressor components.
Numerous modifications have bee developed for improving flow stability through a compressor at low volumetric flow rates because it is desirable to have a wide range of volumetric flow rates in many compressor applications. One such modification is the addition of guide vanes in the inlet to the compressor, wherein the guide vanes vary the flow direction and quantity of entering vapor.
Another modification is to vary the width of the diffuser passage in response to the load on the compressor. Normally, this is done by use of a diffuser movable wall which moves laterally across the diffuser passage to throttle vapor flow through the passage.
Yet another modification involves the use of the variable width diffuser in conjunction with fixed guide vanes. In one type arrangement, the diffuser vanes can be received through complementary-shaped openings in the movable wall of the variable width diffuser. One problem in this arrangement is that the vanes can vibrate in the openings if they are not properly disposed therein, thereby undesirably affecting their performance and useful life.
Another problem with this latter modification involves the clearance between the vanes and openings in the movable wall. Because the vapor pressure increases as the vapor or fluid flows from the impeller through the diffuser passage, the clearances between the vanes and openings allow vapor to flow into the cavity behind the vanes and the movable wall and thus cause an undesirable disruption of flow from the impeller through the diffuser passage, thereby decreasing compressor efficiency.